1. Field of the Invention
The present invention relates to a transmitter which can be tuned over a wide frequency band, in particular a short-wave transmitter, with a filter arrangement which is connected between the output of the transmitter end stage and the transmitter output, in which the filter arrangement comprises sub-filters which are assigned to specific sub-frequency ranges of the transmitter operating frequency and which, in order to suppress undesired harmonics of the transmitter operating frequencies, can be alternatively switched into the signal path of the input end and the output end, via relays, in dependence upon the transmitter operating frequency.
2. Description of the Prior Art
Transmitter devices of the above type are generally known, for example, from the publication "Electronic Components and Applications", Vol. 3, No. 4, Aug. 1981, pp. 210-223 and through the German application No. 33 10 389 Al. Normally in a variable transmitter a filter arrangement consisting of eight sub-octave filters is used for the short-wave band between 1.5 MHz and 30 MHz. Because of the high transmitting power in the order of 1 KW, relays are used to connect the sub-octave filters in dependence upon the transmitter operating frequency because they are moderately priced and suitable for higher switching paths. However, such relays are unsuitable when, as is being increasingly requested by the user, a rapid frequency change is to be carried out, such as is the case, in particular, when a frequency jump procedure is used in order to increase the resistance to interference of a radio connection.
It is, in fact, fundamentally possible to replace the relays by electronic power switches which can carry out a wear-free, rapid switching sequence. However, because of the high switching currents which are required, electronic power switches of this kind involve a considerable technical expense which is of particular significance when several such electronic power switches, namely two power switches, are required in respect of each sub-octave filter.